unify and fix callable phpdoc throughout symfony

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | n/a

I unified the phpdoc to use "callable" as type. It wasn't done consistently. It varied between mixed, callback, callable.
I think callable is best because php 5.4 even has a typehint callable.